This exploratory/developmental application (R34) requests funds to design and pilot an HIV and substance use prevention program for 15 - 18 year-old urban male and female juvenile offenders. High rates of mental health disorders, substance use problems, and risky sexual behavior among these youth underscore the need for comprehensive programs that target their full range of impairment. We will combine and adapt three innovative and empirically supported HIV and substance use prevention programs originally developed for incarcerated drug users (RHAP), runaway youth (Street Smart), and mentally ill adolescents (Project STYLE). RHAP and Street Smart are in the CDC compendium of empirically supported HIV prevention programs. Project STYLE is an ongoing longitudinal HIV prevention program for teens with psychiatric disorders. In stage 1, we will work closely with our advisory board to develop a uniquely tailored manualized intervention for juvenile detainees drawing on RHAP, Street Smart, and Project STYLE. In stage 2, we will pilot test the intervention with a group of 10 males and a group of 10 females remanded to the Cook County Juvenile Temporary Detention Center. We will examine the intervention's feasibility, acceptability and tolerability, and we will evaluate our tracking and retention strategies. We will refine the curriculum and study procedures based on participant feedback and advisory board input. In stage 3, we will test the revised intervention with a larger sample of three groups of 10 male and three groups of 10 female juvenile detainees (N = 60). Participants will complete baseline and 2-month follow-up assessments to evaluate tracking and retention strategies (cohort 1) and preliminary treatment effects (cohort 2). The intervention will be informed by social learning theory and a social-personal framework previously applied to the sexual and drug use behavior of youth in psychiatric care. The intervention will target key determinants of risk taking among young offenders, including mental health problems and emotion regulation deficits, personal attributes (HIV/AIDS and substance use knowledge, attitudes and beliefs about HIV/AIDS; sensation seeking), and peer and partner relationships (peer norms/influence; partner sexual communication). Data analyses will (a) evaluate change in adolescent risky sexual behavior and substance abuse as a function of program participation, and (b) determine the pretest-posttest effect size of program impact on the outcome variables. We will use the effect size to determine the sample size needed for a more definitive test of the intervention in the future. The juvenile justice system is an ideal entry point for HIV and substance use prevention programming. Most offenders return to their communities with inadequate or no discharge planning (e.g., links to community-based health care, substance use treatment), yet empowered with the right tools, they will be better equipped to make safer decisions that reduce the spread of HIV. The long-term goal of the study is to develop an empirically validated, scientifically based HIV and substance use prevention program to reduce health risk behavior among youth in juvenile justice. Consistent with R34 guidelines to support the early phase of intervention development and pilot testing, the final product will form the basis for a full-scale effectiveness study for young offenders. This study is part of an overall program of research designed to understand and prevent HIV infection among high-risk youth.